Fluidic measurement is a critical part of clinical care and homeostasis maintenance. This paper reports feasibility study
of measuring flow velocities over a wide dynamic range using a non-contact measurement technique, optical time-of-flight
(OTOF), with the objective of developing a compact instrument that can be used to measure fluid flow for IV
medication delivery. In this study, a 1480nm laser diode focused to a 20μm spot introduces a heat bolus into the fluid.
This localized temperature increase results in a correlated change in refractive index, detected downstream by observing
defocusing of the visible beam, focused to a 10μm spot in the center of the fluid path. The OTOF measurement provides
the centerline velocity of the fluid flow. CFD modeling ensured that laminar flow was fully developed; prior to the
OTOF measurement point, thus providing a simple, empirical relationship between OTOF and fluid velocity, and hence
volumetric flow rate. Measurements have been performed over a wide range of flow velocity from 1 mm/s to 1 m/s with
approximately ±5% measurement error for broad ranges of fluid properties such as viscosity (0.77-13.88 cp), density
(0.98-1.17 g/cm3) and temperature (5-35 °C). The dynamic range of measured velocity/flow rates is a function of the
distance between the heating and the detection laser beams.